Moving to docker-py, dockerpy-creds and websocket-client from defaults

Same comment made on #74 (closed) is applicable to docker-py and friends. The defaults channel now provides a build of those packages.

Because this is part of beat-devel runtime, we cannot remove already built packages from our stable channel.

But after we drop the recipes, we can bump the dependencies on beat-devel to ensure we use more recent versions from defaults.